Metals including silver, copper, mercury, and zinc are known for anti-microbial properties. Bio-organisms treated by these metals do not acquire resistance to the metals. Therefore, the biocidal metals have advantages over the conventional biocides which often cause the selection of biocide-resistant microorganism.
Silver is generally a safe and effective antimicrobial metal. “Nano-Silver” (or nanosilver) refers to silver particles having diameters predominately less than 100 nm. Often, 80% of the silver in nanosilver is in the form of metallic silver nano-particles. The remaining silver is in ionic form. Because of the small size of the nanosilver particles, the total surface area of the silver exposed is maximized, resulting in the highest possible effect per unit of silver. As a result, 20 ppm concentration of Nano-Silver provides more effectiveness than larger particles of silver solutions, of many times greater concentration.
Nanosilver is commonly known for a number of uses. It serves as an anti-bacterial and deodorizer for fiber, domestic supplies, packing material, cloths, filters, paints, foods, cosmetics and medical products. It prevents electric charging and cut-off of electron waves in electronic products such as cellular phones, computers, semiconductor lines, optical filters, fibers, wallpaper, and glass coatings. Nanosilver is also used as a catalyst, sensor, optical filter, PDP electrode, and LCD Spacer in materials, chemicals, machinery, information and electronic devices.
Recently, Samsung announced that its latest range of refrigerators incorporates a revolutionary new technology called Silver Nano Health System. Since silver has been known for ages to possess natural anti-bacterial properties, utilizing this property of silver, Samsung's range of refrigerators now come with nano scale silver particles coated interior. Ag+ (silver) ions generated from the coating act as a shield against growth of bacterial and other microbial organisms. These ions, due to their inherent anti-bacterial properties, destroy the bacteria and prevent further reproduction, leading to effective protection, of food inside the refrigerator. When silver nano particles come into contact with bacteria, they suppress the respiration of bacteria. This, in turn, adversely affects bacteria's cellular metabolism and inhibits cell growth. The nanosilver in the refrigerator also has strong sterilizing and deodorizing properties which prevent propagation of fungi and bacteria inside refrigerators, helping you enjoy the freshest and cleanest air.
Other nanometals and metallic nanopowders and alloys such as copper, zinc, nickel, cobalt and iron may be substituted for silver and also have similar uses as well as applications in energy, electronics, aerospace and materials.
Although nanometals have truly demonstrated many broad applications, they have not yet been utilized as biocides in building materials. Building materials are subjected to attack by numerous biological organisms, including various molds, fungus and cyanobacteria.
Numerous building materials make use of flexible substrate facers as outer surfaces. A facer is any substrate that is used as an outer surface for insulative or structural materials where such a surface is needed to supply properties not inherent in the material itself. For instance, rigid polyisocyanurate foam roof insulation board, rigid polyisocyanurate foam sheathing board and gypsum sheathing board all use such facers. During the manufacture of such “boards”, the chemical precursors of the polyisocyanurate foam core or gypsum core are poured onto the bottom facer and covered by a top facer. In these cases, the facer is necessary for manufacture, as well as providing a surface to nail to, adhere to, walk on, etc. during installation. Traditionally, such facers have been, and still are, cellulose based. However, cellulose based facers have recently come under scrutiny due to rising concerns about mold in buildings.
Due partly to mold issues, the building industry has moved such products toward fiberglass-based facer products. Such products are usually non-woven fiberglass mats coated with either foamed or highly filled latex coatings. While such coated fiberglass mats are less prone to fungus growth, they too can support fungus growth and said coatings are usually formulated with a biocide. Prior art biocides in coated glass facers include organic biocides such as 2-octylthiazol-3-one (Skane M8 from Rohm & Haas Co., Philadelphia, Pa.) or zinc omadine (Arch Chemicals, Inc., Norwalk, Conn.) or others. Such prior art facer biocides have several disadvantages. First they are not active against all organisms that might attach building products, at the dosages used. Second, they can often be lost through volatilization or degradation at the processing temperatures used to manufacture the facer. Thirdly, some have toxicities that may be harmful to workers during facer manufacture. Finally, they require relatively high amounts of biocide to overcome the first two disadvantages and their use can be very expensive.